PURPOSE: To determine changes in autonomic nervous system activity after treatment in men with lower urinary tract symptoms (LUTS), we evaluated changes in patients\' symptoms, uroflowmetry, and heart rate variability (HRV) after treatment with alpha-blockers for 12 weeks. MATERIALS AND METHODS: Ninety-five men who had LUTS (International Prostate Symptom Score [IPSS] >/=8) were included in this study. We divided them into two groups on the basis of a low frequency/high frequency (LF/HF) ratio of 1.6. After treatment with Xatral XL (Handok Inc., Korea) 10 mg for 3 months, we rechecked their IPSS, uroflowmetry, HRV and compared these with the baseline measurements. RESULTS: Fifty-four men were assigned to the low LF/HF group (group A: LF/HF </=1.6) and 41 men to the high LF/HF group (group B: LF/HF >1.6). At baseline and 12 weeks, none of the parameters differed significantly between the groups except for HF, which is one of the parameters of HRV. IPSS, the IPSS-voiding subscore, and the IPSS-storage subscore decreased and maximal uroflow increased significantly after 12 weeks of treatment. Whereas the baseline LF/HF ratio increased from 0.89+/-0.407 to 1.80+/-1.804 after treatment in group A, it decreased from 3.93+/-5.471 to 1.79+/-1.153 in group B. CONCLUSIONS: The efficacies of Xatral XL were clear in both groups. We found that the LF/HF ratio in the two groups merged to a value of approximately 1.79 after treatment. We suggest that this could be a clue to the importance of balance in autonomic nervous system activity in men with LUTS.